WatNetv2

An improved version of the WatNet. Specifically,

1. The WatNetv2 is not applicable for Sentinel-2 image but also applicable for the Landsat series (Landsat-5, 7, 8 and 9) image.
2. The WatNetv2 achieved improved surface water mapping by comparing with WatNet.

Note:

1. the dataset is prepared at WatSet repository (github.com/Hydrological-Observation-Group/WatSet)

TODO:

1. Rewrite vmamba_seg to one file.
2. try SAM model.
3. replace segmentation decoder to UPerHead for the vmamba.